The present invention generally relates to automatic sprinkler heads and in particular, to thermally responsive assemblies of the type in which a valve is opened at a preset temperature so as to disburse a fire retardant fluid to suppress or extinguish a fire in a designated area.
Automatic sprinkler heads include a valve element which is normally maintained in a closed position by thermally responsive means. Such means include a heat sensitive material such as alcohol or a low melting alloy. One type of such sprinkler heads utilizes a frangible glass bulb filled with alcohol and air. The frangible bulb is disposed between the body of the sprinkler head and a valve so as to maintain the valve in a closed state under normal conditions. When the sprinkler head is exposed to a predetermined elevated temperature, the frangible bulb expands to burst the bulb. This causes the valve to be opened so that a stream of a fire retardant fluid rushes from the outlet of the body. The frangible glass bulb is simple in structure and inexpensive and easy to manufacture. However, the frangible glass bulb may not always be actuated as required at a preset temperature since the responsiveness of the bulb depends on a variety of factors such as the thickness and strength of the bulb and the amount of alcohol and air contained within the bulb.
Another known sprinkler head utilizes a fusible link composed of two metal sheets laminated with solder in a lap joint to form a fusible region. The fusible link extends between two levers. The fusible link provides a retaining force on one of the levers which in turn, provides an upward force on the other lever to hold a valve element in its closed position. In response to elevated temperature, the solder melts to release the levers and thus, the valve element. This allows fluid flow from the sprinkler head. Unlike the frangible glass bulb, the fusible link provides for reliable activation of the sprinkler head as the solder used has a low melting point. However, a disadvantage of such a lap joint type sprinkler head is that the two metal sheets tend to creep away over time. This is due to the fact that the fusible region is subjected to a force by which the valve element is held in its closed position, and another force by which the links and the valve element are brown away when the solder melts.
There has also been proposed a compression type sprinkler head wherein a fusible alloy is normally contained within a fuse holder and held in place by a plunger. When a fire occurs, the fusible alloy melts. This melting causes the plunger to drop. Various components of the thermally responsive assembly are then dislodged from the body of the sprinkler head to allow opening of a valve. This compression type sprinkler head responds reliably in the event of a raise in ambient temperature since it utilizes a low melting alloy as a heat sensitive agent. As a further advantage, the thermally responsive assembly is free from creep since the low melting alloy is constantly pressed within the fuse holder by the plunger.
The melting point of a suitable fusible alloy for most residential and commercial buildings is typically 72xc2x0 C. A fusible alloy having a higher melting point, for example, in the range from 90xc2x0 C. to 190xc2x0 C., will be used in installations where elevated temperatures may be encountered under normal circumstances. Fusible alloys used in the prior art sprinkler heads include lead and/or cadmium. Typically, a fusible alloy having a melting point of 72xc2x0 C. consists of 50 percent by weight of bismuth, 12.5 percent by weight of cadmium, 25 percent by weight of lead, and 12.5 percent by weight of tin. A fusible alloy having a melting point of 96xc2x0 C. consists of 52 percent by weight of bismuth, 32 percent by weight of lead, and 16 percent by weight of tin. Also, a fusible alloy having a melting point of 183xc2x0 C. consists of 37 percent by weight of lead and 63 percent by weight of tin. However, as both lead and cadmium are toxic to the environment, such fusible alloys are banned from land disposal, there is a need for a thermally responsive assembly which is free of lead and cadmium and which can be disposed safely.
Accordingly, it is an object of the present invention to provide a thermally responsive assembly for sprinkler heads which is free of lead and cadmium.
To achieve the foregoing object, the present invention provides an automatic sprinkler head comprising a body having one end adapted for connection to a supply of pressurized fluid and the other end closed by a valve element, and a thermally responsive assembly for normally holding the valve element in a closed position and opening the valve element at a preset temperature to cause the pressurized fluid to flow out of the other end of the body. The thermally responsive assembly includes a holder and a fusible alloy contained within the holder and held in place by a plunger. As a feature, the fusible alloy includes at least two materials selected from the group consisting of tin, bismuth, indium, zinc, gallium and silver.
In one embodiment, the fusible alloy consists of indium and bismuth. This alloy can have a melting point in the range from 72xc2x0 C. to 100xc2x0 C. depending on their content. Alternatively, the fusible alloy may consist of tin, bismuth and indium and can have a melting point in the range from 59xc2x0 C. to 120xc2x0 C. Still alternatively, the fusible alloy may consist of tin, zinc and bismuth and can have a melting point in the range from 130xc2x0 C. to 200xc2x0 C. Gallium and silver may be added to these composite alloys to increase the operating temperature range of the thermally responsive assembly.